1. Field of the Invention
The present invention relates to an ink set, in particular, to an ink set usable for ink jet recording, where ink is ejected from orifices onto a recording medium according to the recording signals. This invention also relates to an ink jet recording method, an ink cartridge, a recording unit and an ink jet recording method using the ink.
2. Description of the Related Art
The ink jet color printing uses water base inks of magenta, cyan, yellow and black, which are prepared by dissolving dyes in a water base medium. In order to improve the durability of recorded images, images formed by the respective color inks must have excellent durability. However, it has been noted that azo dyes and xanthene dyes, which have excellent coloring and are commonly used as a coloring material for magenta ink, tend to have less light-fastness in comparison with other dyes used in other color inks when subjected to a light-fastness test of considerably longer exposure period than usual. It has been also noted that, when a magenta ink containing an azo dye is used with a cyan ink containing a copper phthalocyanine dye that is excellent in light-fastness and tone, fading of the magenta ink becomes conspicuous at the color mixed region in comparison with the region where the magenta dye is used alone. This may lead to the loss of color balance of the image, and hence, considerable deterioration of the image quality.
To solve the above problem, there has been proposed a magenta ink that would not cause photodeterioration where it is mixed with a cyan ink containing a copper phthalocyanine dye. Japanese Patent Application Laid-Open Nos. 2000-109464 (WO 9948981), 2000-169776 (WO 9946341) and 2000-256587 disclose that light-fastness of a magenta ink at a mixed portion with a cyan ink containing a copper phthalocyanine dye is improved by using in the magenta ink a dye having a skeletal structure similar to that used in the present invention.
Another problem in the color ink jet recording is the bleeding phenomenon, that is, when two different inks are adjacently provided on a recording material, they mix at the boundary to reduce the image quality.
In order to improve the light-fastness at the portion where magenta ink and cyan ink are mixed and to prevent bleeding at the boundary, the present inventors have tested various combination of coloring materials, solvents and additives.
They found that when an ethylene oxide adduct of acetylene glycol is added as an penetration-improving agent to prevent bleeding in a magenta ink containing the dye disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-169776 (WO 9946341), and in a cyan ink containing a copper phthalocyanine dye, in addition to the bleeding-preventing effect, the light-fastness at the mixed portion of these inks is improved. In other words, the present invention has been made based on the finding of an unexpected effect of ethylene oxide adduct of acetylene glycol in the magenta ink and the cyan ink, i.e., improvement of the light-fastness at the mixed region of these two inks. Thereby, higher quality images with long durability can be obtained.
The reason why the light-fastness is improved by the presence of an ethylene oxide adduct of acetylene glycol in the magenta and cyan inks is not known yet, but presumed as follows. As shown in FIG. 24, when neither of magenta and cyan inks contain the ethylene oxide adduct of acetylene glycol, they penetrate at a similar rate into the recording medium 2303 in the mixed region, because of the low penetrability. As a result, the coloring materials of magenta and cyan inks are uniformly distributed within a certain depth of the mixed region. On the other hand, as shown in FIG. 23, when the magenta ink and the cyan ink contain an ethylene oxide adduct of acetylene glycol, the penetrability of both magenta ink and cyan ink is improved, so that both inks penetrate deeper into the recording material at the mixed region. The coloring material of the cyan ink (2301), however, has a more planar and bulky structure in comparison with the coloring material of the magenta ink (2302), and therefore, it cannot penetrate into the recording material deeper than the magenta coloring material. Thus the cyan coloring material existing near the surface of the recording material prevents the magenta coloring material that penetrated deeper into the recording material from being irradiated with light, thereby the fading of the magenta coloring material due to light can be alleviated.
Accordingly, one object of the present invention is to provide a new ink set which can form high quality color images with reduced bleeding at a boundary of two inks and with improved light-fastness at a mixed color region of cyan and magenta inks. Another object of the present invention is to provide an ink jet recording method, a recording unit, an ink cartridge and an ink jet recording apparatus for obtaining high quality color images with excellent light-fastness at a mixed color region of cyan and magenta inks.
According to an aspect of the present invention, there is provided an ink set comprising a magenta ink and a cyan ink, the magenta ink comprising a coloring material of the following general formula (I) and a compound of the following general formula (II), and the cyan ink comprising a coloring material having a copper phthalocyanine structure and a compound of the following general formula (II): 
wherein
R1 is a substituted or unsubstituted aryl group,
R2 and R4 are independently a hydrogen atom or a substituted or unsubstituted alkyl group,
R3 is a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, or a halogen atom,
X1 is a carboxyl group or the salt thereof, or sulfonic acid group or the salt thereof;
n is 1 or 2; 
wherein
4xe2x89xa6m+nxe2x89xa620 where m and n are an integer of 0 or larger.
According to another aspect of the present invention, there is provided an ink jet recording method comprising a step of:
ejecting a magenta ink and a cyan ink from orifices onto a recording medium according to a recording signal so as to overlap each other, on the recording medium,
wherein the magenta ink comprises a coloring material of the above general formula (I) and a compound of the above general formula (II), and the cyan ink comprises a coloring material having a copper phthalocyanine structure and a compound of the above general formula (II).
According to another aspect of the present invention, there is provided an ink jet recording apparatus comprising a recording head for ejecting a magenta ink and a cyan ink, wherein
the magenta ink comprises a coloring material of the above general formula (I) and a compound of the above general formula (II), and
the cyan ink comprises a coloring material having a copper phthalocyanine structure and a compound of the above general formula (II).
According to still other aspects of the present invention, there are provided a recording unit and ink cartridge which use an ink set consisting of a magenta ink and a cyan ink, wherein
the magenta ink comprises a coloring material of the above general formula (I) and a compound of the above general formula (II), and
the cyan ink comprises a coloring material having a copper phthalocyanine structure and a compound of the above general formula (II).